Our invention relates to electrodeposition techniques and, more particularly, to the deposition of a selected metal on the cathode of an electroplating cell.
In electroplating, it is often desirable to obtain a uniform thickness of deposited metal on the cathode of the electroplating cell. This uniformity is a function of both composition, operating conditions, potential field, and current distribution over the cell electrodes. Control of the electrolytic solution and the electrode and cell geometry provide a degree of uniformity in cathodic current distribution. It is often necessary, however, to use auxiliary aids to modify the potential field in the cell and to agitate the electrolytic solution to obtain satisfactory results. The restrictions of cell geometry and variations in operating conditions, however, limit the degree of cathodic current uniformity and the resulting uniformity of the metal deposited on the cathode.
Where the surface of the cathode is large, uniformity of cathodic current distribution is difficult to control and the cell operation must be carefully monitored. The preparation of printed circuit boards, for example, requires the uniform deposition of copper over a relatively large surface area. Nonuniformity in the copper deposition results in deleterious electrical and mechanical properties of the printed wiring pattern. To obtain the needed uniformity the placement and geometry of the copper anodes of the cell with respect to the cathode surface to be plated are critical. Additionally, the cell configuration must allow for sufficient agitation of the electrolytic solution. It is an object of the invention to provide uniform deposition of metal on a cell cathode in an economical manner without critical placement of a plurality of cell electrodes or auxiliary devices.